LCD 4 bit and redundant pins


I am using a 16x2 LCD in 4 bit mode and was wondering if it is worth connecting the space pins for the 8bit mode to a logical level?
Dont know if interference on these pins ius significant or not though. But if the are tied to say GND would this prevent any problems?


HD44780 controller chips have internal pullup circuitry on I/O pins, so unused pins can be left unconnected. (See Footnote.)

I would not try pulling them to ground with external connections.

Pulling to ground with resistors could create a problem with an intermediate voltage (neither logic high or low) unless the pulldown is fairly low resistance. This which would consume a little extra power, which is, simply, not called for.

Pulling them to ground with a direct connection might create problems if some errant software command tried to read from the LCD in 8-bit mode, thus creating possible contention with the output drivers' levels.

If you really, really don't want to leave them unconnected, then I'm thinking that it would be OK to pull them up to Vcc with 100K resistors or some such thing, but it's really not necessary.



Just about all low-density text LCD modules are built with '44780 or equivalent components as the logic interface driver. Unless you have a different IC on your module and its manufacturer says that you should not leave unused I/O pins unconnected, I think it's safe to assume that it is functionally and electrically compatible with '44780 circuitry.